1. Field of the Invention
The present invention relates to a battery inspection device for inspecting a condition of a battery by measuring an open circuit voltage of the battery.
2. Description of the Related Art
In the process of manufacturing batteries, such as, for example, rechargeable (secondary) batteries, it may be impossible to completely prevent the mixing of metallic foreign matter into positive electrode material or the like. Mixed metallic foreign matter dissolves in positive electrodes, and is deposited in negative electrodes. Such deposition of metallic foreign matter in negative electrodes may cause occurrence of minute internal short circuiting (hereinafter, referred to as “particle shorts”).
Conventional methods for screening out defective conditions, such as particle shorts, include a method that uses an open circuit terminal voltage (OCV, or Open Circuit Voltage) of a battery, and in which OCVs are measured before and after aging during which spontaneous discharge of a completed battery occurs.
FIG. 5 shows a circuit structure of an inspection system that inspects for particle shorts by measuring OCVs before and after aging during which spontaneous discharge of a battery occurs.
As shown in FIG. 5, the inspection system is formed by connecting, via a pin connector 20, a voltage measurement unit 10 and a fixing jig 30 for fixing one battery stack that includes a plurality of battery modules B1 through Bn to be inspected (hereinafter, simply referred to as “battery module B” where there is no need to distinguish them). In addition to the fixing jig 30, an address switch 40 for setting a jig address to identify the fixing jig 30, or, in other words, to uniquely identify the battery stack to which that jig is attached, is connected to the pin connector 20.
The voltage measurement unit 10 includes selection switches SWa1 through SWan respectively provided for voltage signal lines connected to the battery modules that form the battery stack; an A/D conversion circuit 16 to which open circuit voltage signals of the battery modules output through the voltage signal lines are input, and which converts the input signal into a digital signal; and a CPU 12 to which the digital signal from the A/D conversion circuit 16 is input, and which detects open circuit voltages of the battery modules. The voltage measurement unit 10 further includes a DC signal source that supplies a signal to the address switch 40; and address signal lines for outputting, to the CPU 12, address signals generated by the address switch 40.
As shown in the figure, the address switch 40 is formed by connecting a plurality of switches SWb1 through SWbm in parallel with each other, and a signal line connected to a positive electrode side of the DC signal source is branched off for each of the switches SWb1 through SWbm that form the address switch 40, and is connected to one end of each switch SWb. Another end of each switch is connected in common to a negative electrode side of the DC signal source. The signal line, which is branched off for each switch and connected to each switch SWb, is provided with photocouplers PT1 through PTm that are formed by light-emitting diodes and photodetectors, and output signal lines from the photocouplers are connected in common to the CPU 12. A number “m” of switches SWb that form the address switch 40 can assign an “m” bit address. To set an address unique to each fixing jig, or to each battery stack, the switches SWb of the address switch 40 are turned on or off. For example, by turning on the switch SWb1 and turning off the other switches, it is possible to assign an address having “m” bits, the least significant bit of which is “1” and the other more significant bits are “0”. After the address is assigned by the address switch 40, the selection switches SWa1 through SWan for the voltage signal lines are sequentially turned on or off to thereby sequentially select the battery modules, from which open circuit voltage signals are fed into the CPU 12.
The CPU 12 detects open circuit voltages of the battery modules that form the battery stack which is identified by the address generated by the address switch 40 to store the detected voltages in a memory 50, and detects the degree of drop in open circuit voltages between before and after aging to determine the presence of particle shorts in the battery modules and to further determine whether the battery stack is defective or non-defective.
For an inspection system with such a structure, a battery stack to be inspected is formed, for example, of 30 battery modules, and an address is represented by 15 bits. The address signal lines for outputting address signals to set an address and the voltage signal lines for outputting open circuit voltage signals are independent of one another, and the respective signal lines are housed in one pin connector to output open circuit voltage signals and address signals to the voltage measurement unit 10. Thus, to inspect a battery stack formed of, for example, 30 battery modules, a total of 47 signal lines (30+1 for voltage signal lines and 15+1 for address signal lines) are adequate, and therefore it is sufficient if a pin connector with, for example, 50 pins is used.
However, there has in recent years been a trend for the number of battery modules required in one battery stack to increase. Especially recently, there is a demand for higher power battery stacks to meet requirements from vehicles on which battery stacks are mounted, the number of battery modules included in a battery stack tends to increase, and there is an arising need to efficiently inspect for the presence of particle shorts not only in a battery stack with, for example, 30 battery modules, but also in a battery stack with more than 30 battery modules. For example, when a battery stack is formed of 40 battery modules, a conventional pin connector with 50 pins cannot accommodate address signal lines and voltage signal lines if they are provided independently. Although it is possible to prepare a new pin connector with an increased number of pins, costs will be incurred for preparation of a battery inspection device provided with a new pin connector.
Japanese Patent Laid-Open Publication No. 2002-22778 discloses a device for measuring voltages of multiple storage batteries in which a voltage value detected from a target of voltage detection at the side of a transmitter is transmitted after conversion into time information, and the time information is received at the side of a receiver to convert that time information into a detected voltage value. According to this conventional technique, a power supply line also serves as an information output line so that a reduction in number of cable lines is achieved.
However, this technique disadvantageously requires performing additional processing such as conversion of a voltage value into time information.